Shielded tube and method of making the same



Nov. 8, 1960 H. A. DOWNING EI'AL 2,959,705

SHIELDED TUBE AND METHOD OF MAKING THE SAME Filed Sept. 18, 1952 ALBERTd LALIBERTE.

ATTO

SHIELDED TUBE AND METHOD OF MAKING THE SAlVlE Harry A. Downing, Auburn,and Albert J. Laliberte, West Brookfield, Mass., assignors to AmericanOptical Company, Scuthbridge, Mass., a voluntary association ofMassachusetts Filed Sept. 18, 1952, Ser. No. 310,318

9 Claims. (Cl. 313-313) This invention relates to electricallyconductive shields for electron discharge tubes or the like and hasparticular reference to novel means and method of forming such shieldsand to the improved tube resulting therefrom.

One of the principal objects of the invention is to provide an improvedshielded article such as an electron discharge tube and novel means andmethod of making the same wherein the shield not only functions as aground for the tube but also functions as protective means which rendersthe resultant composite tube structure highly resistant to humidity,corrosion and abrasion, and which is chemically stable, and resistant toextreme temperature changes.

Another object is to provide an electrically conductive shield of theabove character having a controlled resistance.

Another object is to provide a relatively smooth electrically conductiveshield of the above character firmly adherent to the glass envelope ofthe tube and having a hardness which will withstand abrasion by a fingernail or blunt metallic instrument.

Another object is to provide an electrically conductive shield whichwill withstand the above-rnentioned abrasion test after being subjectedto extremely high humidity for long periods of time.

Another object is to provide an electron discharge tube having anelectrically conductive shield thereon which renders the resultingstructure resistant to high and low temperature changes throughoutrelatively long intervals.

Another object is to provide an electron discharge tube with anelectrically conductive shield so controlled as to greatly increase theresistance of the resultant tube to injury by impact or crushing.

Another object is to provide a shielded electron discharge tube of theabove character having greater durability and more general adaptability.

Other objects and advantages of the invention will become apparent fromthe following description taken in connection with the accompanyingdrawings and it will be apparent that many changes may be made in thedetails of construction, arrangement of parts, and steps of the methodshown and described without departing from the spirit of the inventionas expressed in the accompanying claims. We, therefore, do not wish tobe limited to the exact details of construction, arrangement of partsand steps of the method shown and described as the preferred forms onlyare given by Way of illustration.

Ground shields for electron discharge tubes or other similar articlesare not new in the art. Many different attempts have been made, in thepast, to provide tubes of this character with electrically conductiveshields to reduce the capacity between certain tube elements, to shieldthe tubes from other circuit elements and to provide external shieldgrounding means for such tubes.

It has been found, however, that such prior art shields, while efiicientas electrically conductive means, were not acceptable for use underdifferent temperature and at- A States Patent mospheric conditions orwere not chemically stable or abrasion resistant. Another factor which,as far as is 'known, has not been considered is that of increasing theresistance of the inherent tube to impact or crushing as well asproviding the tube with an electrically conductive coating.

The present invention, therefore, is directed to providing an electrondischarge tube or similar article with an electrically conductingcoating possessing characteristics for overcoming all of the prior artdifiiculties in a simple, efficient and inexpensive manner whileproviding the tube with means for increasing its resistance to impactand crushing.

Referring to the drawings:

Fig. 1 is a side elevation of a tube embodying the invention; and

Fig. 2 is an enlarged sectional view taekn as on line 2-2 of Fig. 1 andlooking in the direction indicated by the arrows.

Referring to the drawings, the tube 4 embodying the invention comprisesa glass envelope 5 in which is encased its operative components A. Aplurality of leads 9, operatively associated with the respectivecomponents A, are extended outwardly through the base 11 of the tube.The glass envelope has an outer roughened surface 6 formed thereon andfurther has a coating 7 of an electrical conductive metal formed on saidsurface. The coating 7 and the roughened surface 6 are in mechanicallybonded relation with each other. An outer coating 8 of a metalparticularly resistant to abrasion, and which renders the resultantcomposite structure further resistant to varying atmospheric andtemperature changes, resistant to high humidity and having a controlledelectrical conductivity is formed on the inner coating 7. The outercoating 8 and inner coating 7 form a composite shield which in additionto the above characteristics is so controlled as to greatly increase theresistance of the tube to injury by impact or crushing.

In carrying out the invention, the leads 9 as well as a controlledportion of the ground lead 10 and base 11 of the tube are provided withan acid protective coating such as paraffin or other stop off lacquer.The tube is then immersed in an etching solution from five to thirtyseconds to produce a desired roughened outer surface thereon. An etchingsolution which has proven satisfactory is as follows:

10 grams BaSO --Bariurn sulfate 4 grams (NH SO --Arnmoniurn. sulfate 4grams NH HF Ammonium bifluoride 16 grams C H (OH) Glycerol 2 grams H C OOxalic acid 4 grams H 0Water If desired, instead of roughening thesurface by etching, the said surface may be sand-blasted or otherwisetreated to produce the desired roughening. It has been.

found, by actual tests, that the toughening of the surface by acidtreatment does not weaken the envelope of the tube to crushing.

- When roughened by acid etching, the tubes are rinsed in distilledwater and completely freed from residual acid. A continuance of theprocess may be carried on either with the tube in a wet or dry state.The tube, however, is preferably dried for purposes of examining theroughened surface. Following the roughening process, the tubes aretreated with a sensitizing or fluxing solution. This is preferablyaccomplished by scrubbing or rubbing the roughened surface of the tubewith solution saturated absorbent cotton or other suitable means. Asensitizing or fluxing solution which has been found to produce de-'sirable results is formed by dissolving stannous chloride (SnCl in anequal amount by weight of hydrochloric 3 acid (Hcl) and diluting to fivepercent with distilled water (H O).

Following the rinsing of the tubes with distilled water, they areprovided with an electrically conductive coating of silver which ispreferably deposited by a dual spraying method.

This coating may be applied by making a solution of ammoniacal silvernitrate which is a mixture of chemically pure silver nitrate andchemically pure ammonium hydroxide (28-29% NH OH). A second solution ismade of dextrose or formaldehyde dissolved in distilled water, with theamount of dextrose or formaldehyde in the solution being controlledaccording to the percentage of silver in the ammoniacal mixture in orderto bring about the proper chemical reaction during the dual sprayingmentioned above. The solutions are used with a spray gun having dualspray nozzles, each of which is coupled with separate containers inwhich the respective solutions are placed. The two spray nozzles are sorelated as to form an intermingling mist of said two solutions whereupona chemical reaction takes place in such manner that a substantiallyuniform coating of silver is deposited on the glass tube surface. Thisproduces a substantially uniform coating of silver in suflicientthickness to produce desired electrical conductivity and which is firmlyadherent to the roughened surface of the tube. This coating, althoughelectrically conductive, is susceptible to chemical reaction orweathering and is insufiiciently resistant to scratching. It merelyfunctions as a forerunner for an electrolytically deposited outersurface of nickel, rhodium, chromium or other similar non-corrosive,hard and abrasion resistant metal which is to be subsequently depositedon the outer surface thereof.

The silver coating is such that the outer subsequent electrolyticallydeposited metal will be smooth and of relatively uniform thickness andwill firmly adhere and bond therewith.

The composite coating, due to the outer electrolytically depositedlayer, is not only resistant to scratching or abrasion but also rendersthe resultant composite tube structure more chemically stable andresistant to weathering, atmospheric and temperature changes as well asresistant to exposure to humidity.

Although the silver coating has been described above as being applied bya dual spray method, a suitable silver coating might be deposited in thefollowing manner:

A silver solution is formed comprising:

13.52 oz. of water (H O) 0.71 oz. of silver nitrate (AgNO 0.35 oz. ofpotassium hydroxide (KOH).

To this solution, 50 ccs. of ammonium hydroxide, (NH OH specific gravity0.90) is added. To the above mixture is further added 0.07 oz. of silvernitrate dissolved in 1.01 oz. of water. The above solution is designatedsolution A.

A reducing solution is formed as follows:

33.81 oz. water 3.17 oz. sugar 0.14 oz. nitric acid (specific gravity1.42).

This solution is designated B.

The glass envelopes of the tubes which have been acid-etched andsensitized, as described by the firstrnentioned silvering process, arethen suspended in distilled water in a suitable container. Equal amountsby volume of solutions A and B are then mixed and immediately pouredinto the water having the glass envelopes of the tube suspended thereinwhereupon the chemical reduction of thesilver salt by the reducing agentresults in the deposition of the silver on the outer surface of thetube.

I Due to the fact that the silver coating, as formed by either of theabove methods, is firmly adherent with the roughened surface of the tubeand that the outer finally deposited metal firmly bonds with the silver,the said resultant shield will be held in proper anchored relation withthe tube. In order to more positively retain the anchored relation ofthe shield with the tube, the tube is initially formed to a controlledcontour shape which is such as to have substantially parallel sides 12and 13 terminating adjacent the lower portions thereof in converging orinwardly curving portions 14 and 15 extending throughout the perimeterof the tube and which, in turn, terminates in an outwardly flared lowerbase portion 16. This controlling of the initial shape of the tubeenvelope and the fact that the outer and inner metallic coatingsinherently conform to the outer contour shape of the tube further addsto the anchoring action thereof with the tube. The thickness of theouter shield is further controlled so as to render the resultant tubemore resistant to fracture or crushing while providing the desiredelectrical conductivity. It has been found that for a coating rangingfrorn one to three thousandths of an inch in thickness that theresistance of the resultant tube to fracture and crushing, as comparedwith the inherent glass envelope of the tube, has been approximatelydoubled, depending upon the actual thickness of the nickel coating.However, it has been found that the metal shield on the tube has aresistance to fracture and crushing of approximately ten to one ascompared with the inherent glass envelope of the tube. The coating is soformed as to overlie and have electrical contact with the upper tubeencircling portion 17 of the ground lead 10 and will function as meansfor permanently retaining the ground lead in desired position on thetube. The electrolytic process may be any of the commonly known typesand is preferably carried out by standard procedures.

A solution of the type giving a hard and desirable deposit is asfollows:

Material Formula Solution,

ozjgal.

Nickel snlite hept hydrate NiSOLT ZO 32. 0 Ni kel chloride hexihydrateNiClLG bO 4. 0 S"diumfor'n te NaHGOz 5. 0 Crbalt s 11f te he tahydrsteCOSO4.7TIQO (I. 6 Am nanium sulfite (NHthSOi 0.10 Forrn 'ldehyde TTCWO0. 33 BOIIC Acid H3130: 4. 0

having a pH factor of approximately 3.7, cathode current density 7 toamps. per square foot, temperature to F. with suitable agitation. Theabove is a formula set forth in Louis Weisberg and William B. Stoddard,Jr., Patent No. 2,026,718, issued January 7, 1936. The above patent alsogives additional formulae which might be employed.

Another plating solution which has produced desirable results is asfollows:

Brightener No. 1-RL, Brightener No. 3, and Non Pitter No. 22 are madeand sold by The Udylite Corporation, 1651 East Grand Building, Detroit11, Michigan.

A brightener which might be used may be selected from the followinggroup:

Benzyl naphthalene sodium sulfonate as set forth in Lutz and WestbrookPatent No. 1,818,229;

Complex lead citrate as set forth in Pinner Patent No.

1,837,835; Sulfuric acid reaction products of oleoresins and naturalresins as set forth in Pine Patents Nos. 2,029,386 and 2,029,387;

Reaction products of alkali metal cyanides and certain.

aldehydes and ketones as set forth in Hull Patent No.

Zinc or cadmium plus naphthalene-sulfonic acids as set forth in WaitePatent No. 2,112,818;

Selenium plus sulfonates as set forth in Harshaw and Long Patent No.2,125,229;

Cd or Zn plus sulphonamides or suphonimides as set forth in Brown PatentNo. 2,191,813;

Halogenated aldehydes as set forth in Brown Patent No.

Sodium formate as set forth in forth in Baker Patent No.

Aminopolyaryl methane plus naphthalene sulfonate as set forth in Lind,Harshaw, and Long Patent No. 2,198,267;

Aminopolyaryl methane plus single ring aryl sulfonamides and sulfimidesas set forth in Lind, Harshaw, and Long Patent No. 2,198,268;

Azo compound plus naphthalene sulfonates, single ring aryl sulfonamides,or single ring aryl sulfimides as set forth in Lind, Harshaw, and LongPatent No. 2,290,- 342;

Aromatic amino compounds plus an organic compound characterized by aductilizing tendency as set forth in Lind, Harshaw, and Long Patent No.2,238,861;

Safranine compounds plus ortho benzoic sulfimide (saccharin) and itssalts as set forth in Lind, Harshaw, and

Long Patent No. 2,326,999;

Mercaptopyrimidines as set forth in Ter Horst Patent Starchates as setforth in Gaver Patent No. 2,406,072;

Sulfonated arylaldehydes as set forth in Stocker and Freed Patent No.2,409,119; and

Thiourea as set forth in Stocker and Freed Patent No.

Optimum brightness and brightener stability depend upon properinterrelationship between solution formulation, temperature, pH andcurrent density and all of these factors must therefore be carefullyconsidered. The use of a brightener is of minor importance as it dealsprimarily with the resultant appearance of the outer coating and has noeffect as to its main functional characteristics.

A non-pitter which may be employed is hydrogen peroxide, formaldehyde orany other suitable surface-active agent and the amount thereof iscontrolled according to the base formula as commonly known.

Although the initial silver coating has been described as preferablybeing deposited by a particular chemical reduction, it might be appliedby other known methods or techniques if properly controlled so as toobtain a coating having the relatively smooth, uniform texture asobtained by the chemically reacted mists process described herein.

The inner conductive coating 7 has been referred to as being silver.However, other coatings of conducting materials such as a chemicaldeposition of copper may be utilized. This could be accomplished byreducing copper from a fluohorate solution as set forth in Narcus PatentNo. 2,454,610. To accomplish this, the roughened surface of the glass iscleansed by a suitable proprietory cleaner such as soap. The surface isthen sensitized through the use of a solution embodying approximately 50ccs. of titanous chloride, 50 ccs. hydrochloric acid, and 1000 ccs.distilled water. After the surface has been so activated, and afterthoroughly rinsing the article in clean water, the article is thensubjected to a so-termed seeding solution. This is accomplished throughthe use of a dilute solution of chloroplatinic acid made up of 1 gram ofchloroplatinic acid per gallon of distilled 6 water with five to tenminutes immersion. The article is then transferred directly to asolution made up by mixing equal weights of a copper solution and areducing Although only silver and copper have thus far been disclosed asbeing suitable for the base electrically conductive coating 7, othermetals such as platinum, gold or the like might be employed and appliedby conventionally known methods if properly controlled to obtain thedesired result.

Instead of using metal, the inner conductive coating may be formed ofgraphite applied by known methods but controlled in accordance with theend result desired. It has been found that due to the rough texture ofthe outer surface of the glass envelope, the graphite might be applieddirectly to the surface by rubbing it into said surface to a uniformlysmooth texture. Another method has been to apply a lacquer or othertacky substance to the surface and then dip the tube into powderedgraphite. Here again, the graphite is rubbed to a uniformly smoothtexture. The use of an undercoating of this nature makes it possible toelectrolytically deposit the outer coating 8 on the envelope of thetube.

However, the silver coating, as first described, has thus far provenmost desirable.

In all instances, the outer protective coating is applied by anelectrolytic process.

Subsequent to the forming of the final surface on the tube, the paraffinor other stop off lacquer is removed. This parafiin or stop off coatingmay, however, be allowed to remain on the tube as protective means untilit is ready for actual use. This paraffin or other stop off lacquer isused in all of the above-described coating techniques and not onlyprotects the leads 9 from the acid but also restricts the coatings atthe lower end of the tube in such manner as to prevent their forming ashort across said leads.

From the foregoing description, it will be seen that a novel shieldedtube as well as simple, eificient and economical means and method ofmaking the same have been provided.

Having described our invention, we claim:

1. An electron discharge device comprising an envelope in which isencased the operative components of said device and having a basethrough which leads to said operative components extend, said envelopeconstituting a thin frangible glass wall covered by a thin coatingembodying an outer layer of a hard, abrasion and corrosion resistantmetal bonded to the surface of said glass wall by means of an inner filmof softer and less inert but more highly electro-conducting material,said inner film being mechanically interlocked with said surface of theglass wall and grounded to one of the leads in the base to electricallyshield the operative components of said device, and said outer layerserving to protect said shielding film and to increase the resistance ofthe envelope to fracture and crushing, the metal of said outer layerbeing chemically stable and generally inert so as'to impart to thedevice a resistance to temperature change and humidity.

2. An electron discharge device comprising an envelope in which isencased the operative components of said device and having a basethrough which leads to said operative components extend, said envelopeconstituting a thin frangible glass wall covered by a thin coatingembodying an electrolytically deposited outer layer of a hard, abrasionand corrosion resistant metal bonded to the surface of said glass wallby means of an inner film of softer and less inert but highlyelectro-conducting material, the surface of said glass wall beingroughened and the film being interlocked with the irregularities of saidsurface, said film being grounded to one of the leads in the base toelectrically shield the operative components of said device, and saidouter layer serving to protect said shielding film and to increase theresistance of the envelope to fracture and crushing, the metal of saidouter layer being chemically stable and generally inert such as toimpart to the device a resistance to temperature change and humidity.

3. An electron discharge device comprising an envelope in Which isencased the operative components of said device and having a basethrough which leads to said operative components extend, said envelopeconstituting a thin frangible glass wall covered by a thin coatingembodying an outer layer of a hard, abrasion and corrosion resistantmetal from the group consisting of nickel, chromium and rhodium which isbonded to the surface of said glass wall by means of an inner film ofsilver which issofter and less inert but more highly electroconductingthan the metal of said outer layer, said film being mechanicallyinterlocked with said surface of the glass wall and grounded to one ofthe leads in the base to electrically shield the operative components ofsaid device, and said outer layer of metal serving to protect saidshielding film of silver and to increase the resistance of the envelopeto fracture and crushing, the metal of said outer layer beingsufficiently chemically stable and generally inert as to impart to thedevice a resistance to temperature change and humidity.

4. An electron discharge device comprising an envelope in which isencased the operative components of said device and having a basethrough which leads to said operative components extend, said envelopeconstituting a thin frangible glass wall covered by a thin coatingembodying an outer layer of nickel which is a hard, abrasion andcorrosion resistant metal, said layer being bonded to the surface ofsaid glass wall by means of an inner film of silver which is softer andless inert but more highly electro-cond'ucting than the nickel, saidfilm being mechanically interlocked with said surface of the glass walland grounded to one of the leads in the base to electrically shield theoperative components of said device, and said outer nickel layer servingto protect said shielding film of silver and to increase the resistanceof the envelope to fracture and crushing.

5. An electron discharge device comprising an envelope in which isencased the operative components of said device and having a basethrough which leads to said operative components extend, said envelopeconstituting a thin frangible glass wall covered by a thin coatingembodying an outer layer of a hard, abrasion and corrosion resistantmetal and an inner film of softer and less inert but more highlyelectro-conducting material from the group consisting of gold, silver,copper and graphite, said inner film being mechanically interlocked withsaid surface of the glass wall and grounded to one of the leads in thebase to electrically shield the operative components of said device, andsaid outer layer being electrolytically deposited on said film andserving to protect the film and to increase the resistance of theenvelope to fracture and crushing, the metal of said outer layer beingchemically stable and generally inert so as to impart to the device aresistance to temperature change and humidity.

6. An electron discharge device comprising an envelope in which isencased the operative components of said device and having a basethrough which leads to said operative components extend, said envelopeconstituting a thin frangible glass wall having an acid etched surfacecovered by a thin coating embodying an outer layer 'of a hard, abrasionand corrosion resistant metal and an inner film of a softer and lessinert but highly electroconducting material from the group consisting ofsilver, gold, copper, and graphite, said inner film being mechanicallyinterlocked with said acid etched surface of the glass wall and groundedto one of the leadsin the base to electrically shield the operativecomponents of said device, and said outer layer serving to protect saidshielding film and to increase the resistance of the envelope tofracture and crushing, the metal of said outer layer being chemicallystable and generally inert so as to impart to the device a resistance totemperature change and humidity.

7. An electron discharge device as claimed in claim 6 wherein said outerlayer comprises an electrolytic deposit of a metal from the groupconsisting of nickel, rhodium and chromium.

8. An electron discharge device comprising an envelope in which isencased the operative components of said device and having a basethrough which leads to said operative compbnents extend, said envelopeconstituting a thin frangible glass wall having a roughened outersurface, a thin film of highly electro-conducting material interlockedwith the irregularities of said roughened surface and presenting asubstantially smooth surface, and a uniformly thin layer of metal fromthe group consisting of nickel, chromium and rhodium electrolyticallydeposited on said film surface, the film of highly electro-conductingmaterial being grounded to one of the leads in the base to electricallyshield the operative components of the device, and said outer layer ofmetal being hard, abrasion and corrosion resistant and otherwisegenerally inert and chemically stable in comparison to the inner film ofhighly electro-conducting material to impart to the device a resistanceto temperature change and humidity.

9. An electron discharge device comprising an envelope in which isencased the operative components of said device and having a basethrough which leads to said operative components extend, said envelopeconstituting a thin frangible glass wall having a roughened outersurface on which is chemically deposited a thin film of highlyelectro-eon'ducting material from the group consisting of copper, gold,silver and graphite, said film being interlocked with the irregularitiesof said roughened surface and presenting a substantially smooth surfaceto which is strongly bonded a uniformly thin electrolytically depositedlayer of metal from the group consisting of nickel, chromium andrhodium, the film of highly electro-coriducting material being groundedto one of the leads in the base to electrically shield the operativecomponents of the device, and said outer layer of metal being hard,abrasion and corrosion resistant and otherwise generally inert andchemically stable in comparison to the inner film of highlyelectro-conducting material to impart to the device a resistance totemperature change and humidity.

References Cited in the file of this patent UNITED STATES PATENTS928,224 Shoemaker et al. July 13, 1909 1,128,817 Pickard Feb. 16, 19151,731,797 Strongson Oct. 15, 1929 1,802,371 Bullivant et a1 Apr. 28,1931 2,214,646 Walker Sept. 10, 1940 2,421,079 Narcus May 27, 19472,424,583 Rahm July 29, 1947 2,464,270 Spencer Mar. 15, 1949 FOREIGNPATENTS 473,385 Great Britain Oct. 12, 1937 OTHER REFERENCES MetalFinishing, September 1944, pages 534 to 538.

